Esterification: Definition, Process & Reactions

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  • 0:03 Definition
  • 1:16 Esterification Process
  • 2:17 Esterification Reactions
  • 3:07 Lesson Summary
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Lesson Transcript
Instructor: Laura Foist

Laura has a Masters of Science in Food Science and Human Nutrition and has taught college Science.

In this lesson, we'll learn about esterification, which means we'll define necessary terms to understand esterification, explain the process that chemicals undergo to form esters, and look at examples of reactions that use esterification.

Definition of Esterification

If you were out playing basketball and rolled your ankle, you may take aspirin to relieve the pain and swelling. Aspirin relieves swelling and pain with a compound called salicylic acid, yet the carboxylic group in salicylic acid greatly irritates the stomach. Chemists discovered that if it is combined with acetic acid then it forms an ester, acetylsalicylic acid, which reduces the irritation on the stomach. This is the compound that we take as aspirin.

The reaction that combined the salicylic acid and acetic acid to form acetylsalicylic acid is called esterification. Esterification is the process of forming esters from carboxylic acids. An ester is when a carbon is connected to two oxygens, but one of the oxygens isn't connected to anything else (so it is double-bonded to the carbon), while the other oxygen is connected to another carbon. Here is the general formula for an ester ('R' refers to a carbon chain):


A carboxylic acid is very similar to an ester, except the second oxygen is not connected to another carbon; it is just connected to a hydrogen atom. An alcohol is a carbon that is connected to an -OH group (or oxygen connected to hydrogen).

The Esterification Process

Esterification occurs when a carboxylic acid reacts with an alcohol. This reaction can only occur in the presence of an acid catalyst and heat. It takes a lot of energy to remove the -OH from the carboxylic acid, so a catalyst and heat are needed to produce the necessary energy.

Once the -OH has been removed, the hydrogen on the alcohol can be removed and that oxygen can be connected to the carbon. Because the oxygen was already connected to a carbon, it is now connected to a carbon on both sides, and an ester is formed.

The methyl acetate that was formed is an ester. In this image, the green circle represents what was the carboxylic acid (in this case acetic acid), and the red circle represents what was the alcohol (in this case methanol):

Methyl acetate

This reaction lost an -OH from the carboxylic acid and a hydrogen from the alcohol. These two also combine to form water. So any esterification reaction will also form water as a side product.

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